Conventionally, a blow-by gas recirculating apparatus for an engine is known in which a PCV valve is attached to a head cover attached to a cylinder head, the PCV valve is communicated with a downstream intake passage of a throttle valve through a blow-by gas passage, and an upstream intake passage of the throttle valve is communicated with a crankcase through a fresh air introducing passage (see Patent Literature 1).
An apparatus of this kind has an advantage that the blow-by gas in the crankcase is recirculated to a combustion chamber by ventilation in the crankcase, and the blow-by gas is suppressed from entering engine oil collected in a lower portion of the crankcase to degrade the engine oil.
In this prior art, however, the fresh air introducing passage is communicated with the crankcase through the head cover, and hence there arises a problem.